Pattern recognition systems have been proposed in which stored reference images are correlated with input images.
For example, U.S. Pat. No. 3,716,301, issued Feb. 13, 1973, to Caulfield, et al., describes a fingerprint identification apparatus in which a user presses a finger against an input prism (prism 14), and a laser beam is reflected from the input prism's surface to generate an input image representing the Fourier transform of the finger image. The input image is then correlated with a reference image having been recorded in an already prepared hologram of the said transform. At column 5, lines 57-62, Caulfield, et al. teach use of a mechanically rotating dove prism to compensate for misalignment of the user's finger with respect to the input prism. At column 7, lines 28-66, Caulfield, et al. also teach use of a prerecorded Fourier transform hologram representing two or more reference images (each having a different rotational orientation) and presentation by the user of two different input images (each having a different orientation).
U.S. Pat. No. 4,227,805, issued Oct. 14, 1980, to Schiller, describes another pattern recognition system. In the system of U.S. Pat. No. 4,227,805, the user's finger rests in a linearly translatable carriage (carriage 20), and is scanned by a laser beam as the carriage translates linearly. The laser beam is reflected from a surface of the carriage, and the reflected beam is passed through a lens to generate an input image representing the Fourier transform of the finger image. The input image is then correlated with a reference image as it propagates through a prerecorded Fourier transform hologram (hologram 34).
However, the use of mechanically moving components in conventional correlation systems (such as the rotating Dove prism of U.S. Pat. No. 3,716,301, and the translating carriage of U.S. Pat. No. 4,227,805) undesirably causes noise due to vibration of the moving components. Furthermore, the mechanical motion is undesirably slow, so that scanning time required for producing a single correlation signal is undesirably long.
It has been proposed that pattern recognition systems of the correlation type be employed in lock devices. For example, U.S. Pat. No. 2,936,607, issued May 17, 1960, discloses a lock apparatus in which a user's fingerprint is electronically correlated with a stored reference fingerprint image.
However, it has not been known until the present invention how to design or operate a holographic locking device in which an input image is correlated in real time with an already prepared Fourier transform hologram (representing a single reference image), without employing mechanically moving components. Nor has it been known how to implement a two-stage holographic locking device in which correlation between two input images and two prerecorded reference images is performed rapidly and accurately in order to open a lock, and which does not employ moving mechanical parts.